1. Field of the Invention
The present invention relates generally to the field of lens systems, and specifically, to a compact digital camera objective having interdigitated element alignment, stray light suppression, and anti-aliasing features.
2. Background Information
Prior art complex lens systems with a f/2.0 relative aperture and a 50 degrees field of view that cover color applications (e.g., white light applications, visual applications, film applications, etc.) typically require six lens elements in high index optical glasses with doublet construction in at least two groups of lens elements to provide control of (axial and lateral) chromatic aberrations. Chromatic aberrations are typically severe for plastic lenses and there are only a limited number of materials to choose from. The doublet construction typically includes a positive lens element that has a low dispersion material (e.g., crown) and a negative lens element that has a high dispersion material (e.g., flint) coupled together. However, the disadvantage with prior art lens systems is that the doublet construction in the two groups of lens elements requires two extra lens elements which is very expensive to produce. Moreover, a lens system with six lens elements cannot be made as compact as a lens system with four lens elements.
Accordingly, there is a need in the art for a method and apparatus to provide a complex lens system that is compact and inexpensive while correcting chromatic and all other optical aberrations.
In addition, complex lens systems that operate in the f/2.0 relative aperture, 50 degree full field diagonal and have a small imaging device format (e.g., less than an 8.0 mm diagonal) require very sensitive fabrication and assembly tolerances for acceptable "as-built", image quality. The prior art lens systems typically align lens elements by using spacers. The disadvantage with using spacers is that they add to the cost of the lens system and require a high degree of accuracy in assembly of the lens system.
Therefore, there is a further need in the technology to provide interdigitated alignment between lens elements without the need for extra parts while facilitating construction of the lens system. There is also a need to suppress stray light from reaching a detector array in a lens system that includes interdigitated single piece lens elements having an optical portion and a non-optical mechanical flange portion.
A further problem with optical systems that form images on detector arrays (e.g., a charge-coupled detector, "CCD") and discretely sample images is that they produce aliasing effects in the displayed image. An example of aliasing effects is Moire effects which occur when objects move, change patterns, and/or change color relative to the detector array and have dimensions commensurate with the pixel dimensions of the detector array. One solution for eliminating or minimizing aliasing effects is to add a quartz plate in front of the detector array. The quartz plate blurs and reduces the sharpness of the image just the right amount to minimize such aliasing effects. However, quartz plates are very expensive, virtually costing as much as the lens system.
It is therefore desirable to provide an optical lens system that eliminates aliasing effects while maintaining a low cost.